IV. Manufacturing Resource Positioning Methods
4.2 Workspace estimation using the operation data of overhead cranes
4.2.2 Relative positioning of a product
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the line of sight is blocked. If a loading process is operated at this moment, the operation information is lost and this lost is fatal to process monitoring.
The acoustic signal positioning method doesn’t need additional transmitter when using an original noise of the facility. This advantage makes management easy and the installation cost lower. If additional acoustic signal generator is installed at the target, data transmission is possible and it can be used for identification or fault diagnosis. In addition, if the non-audible frequency can be generated from the acoustic signal generator, the operator is not disturbed by the noise problem. A lot of things should be studied before applying these advantages to the overhead crane. For this reason, acoustic signal positioning method is not proper for the overhead crane positioning now. However, we focused on the advantage that it can be applied to other manufacturing resources, and this study is described in the Chapter 4.3.
In conclusion, among those trolley positioning methods, encoder, barcode distance meter, marker, and light emitting diode methods can measure the highly accurate distance or speed of trolley in low cost. Those 4 methods have different characteristics that are problematic when applied to the overhead crane. Barcode and marker methods need ongoing management to reduce the pollution problem. Light emitting diode method doesn’t work properly when the line of sight is blocked. The problem in the encoder method can be solved with giving reference for the calibration. Finally, we selected an encoder method for the trolley positioning that applied a solution for the calibration problem.
Main panel forms the spatial basis of a curved-block. The moving plane of the trolley is parallel with the ground and in this plane, preformed spatial basis with main panel is rarely changed. At this point, coordinate information of the main panel can be used to form the workspace of a curved block.
However, the coordinate information of the parts is recognized like the Figure 4.6 below, part grouping and product workspace estimation is needed.
Figure 4.6: Coordinate information of loaded parts
Part grouping and product workspace estimation
We developed part grouping and product workspace estimation method using loading coordinate and weight of the parts. This method was developed under the following assumptions.
Loading position is acquired as perpendicular x and y coordinate information
Main panels are preloaded before the other parts
Thicknesses and densities of the main panels are same
After a panel is loaded, physically neighbor panel is loaded in the next order
Shape of the blocks in top-view is fixed as a square
Workspaces of the curved-blocks are spaced apart
Assuming that thicknesses and densities of the main panels are same, they have an area proportional to the weight. Final shape of the block in top-view is assumed as a square, and its length of one side equals root of the total weight. Part grouping and product workspace estimation are processed as the following figures.
If the part loaded in the empty workspace, it is regarded as a first main panel of a new block and it has a virtual area which is proportional to the weight. When a virtual area of newly loaded part overlaps with the virtual area of first main panel, those two panels are grouped and used to estimate the
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(a)(b)
Figure 4.7: Principle of the workspace estimation
(a) (b)
(c)
Figure 4.8: Example of the workspace estimation in a shop-floor
When a virtual area of newly loaded part overlaps with the virtual area of a product not the first main panel, newly loaded part is grouped with two prior panels and used to estimate the virtual area of product as displayed in the Figure 4.7 (b). The newly estimated virtual area of product has a weight of the sum of the weight of third main panel and prior two main panels, and has an area proportional to the weight.
Through this part grouping and estimation method, loaded main panels are grouped and used to estimate the workspace of the product. Even the shape of each main panel is not a square, final estimation of the product area is matched with a square and this process is exampled in the Figure 4.8.
Furthermore, for the several cases, this method has the exceptional rules. First, after all main panel is loaded, part grouping is keep processing but a newly loaded part is no longer considered as a main panel.
As exampled in the Figure 4.9 (a), workspace expansion also stops due to the weight summation stops.
The point of the main panel loading stops is determined by the grouping method for the product identification described at the Chapter 3.4.2. The next exceptional case is displayed in the Figure 4.9 (b).
(a) (b) Figure 4.9: Exceptional cases in the workspace estimation
A virtual area of newly loaded part overlapped with a virtual area of product. If the main panel loading is in progress, this newly loaded part should be considered as an additional main panel. However, if the area also overlaps with another block, the block containing the center of mass has priority for the grouping.
Workspace estimation in the ship block assembly monitoring system
The ship block assembly monitoring system described at the Chapter 3.5 is simulated with the part
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in real-time and displayed it on the user interface like the Figure 4.10. Virtual areas of the products are displayed in red, and a newly loaded part is displayed in green.
Figure 4.10: The visualized workspace estimation method on the user interface
Curved-block workspace can be estimated by applying encoder on the overhead crane and using workspace estimation method. Matching this estimated workspace with spatial schedule can be used to the production progress measurement and the operation guide. However, only with the weight data, this method can be applied when a shape of the product in top view is square. Furthermore, this method is dependent on the process sequence so change of the sequence interrupts the grouping and the workspace area estimation such as loading outfitting before the main panel. To solve these problems and improve the method, additional information is needed as in case of production progress measurement.